Andrew Marr: You've coined terms like "the underclass" and "the new rabble" and you've made much of illegitimacy. Why do you think illegitimacy is so important?

Charles Murray: Illegitimacy is important for the socialisation of little girls and especially little boys. If you have large numbers of young men growing up who never see an adult male doing the ordinary things men do, then you get chaos. This is not a moral statement, it's an empirical statement. We've had a chance to watch it in the US, especially in the black community, where we've had very high rates of illegitimacy now for 20 or 30 years.

There are an awful lot of people who are in families but out of wedlock. There is a male figure, but they're not married.

I've heard this argument a lot in Britain, but I think you've got to take a harder look at your own situation. We know that cohabitation in Britain is pretty brief on average, a matter of a couple of years. We don't know whether these males who cohabit behave like fathers. And we know from the States that surrogate fathers, who are not the biological father, are very problematic.

Why are they problematic?

There's a big difference in outcomes between children who grow up without a father and children who grow up with a married set of parents.

You make a connection between single-parent families and welfare, but in fact the vast majority of them are not on welfare, they're actually doing OK. They're two-thirds or half way up the income scale.

That's not true in the US. There is a large gap between the rates of illegitimacy among women who are below the poverty line before they give birth, and women who are above the poverty line.

I'm still confused as to why you focus on the welfare state as the problem here.

You don't have to explain why women want to have babies, or why young men want to sleep with young women. Those things are very powerful drives, and various penalties have helped to restrict their incidence: social stigma, religion, economic factors. But what you need is a situation in which a young woman's own parents are saying to her: "You'd better not get pregnant, girl, because we can't afford it." What the welfare system does, in effect, is cushion that short-term economic problem, remove one of those major blocks. And in an era when the religious and social stigma is also vanishing.

And your solution is simply to take welfare away from single mothers?

Yes, in a word.

What really worries me about this is the spectacle of children living in extreme poverty. You talked about this originally as your thought experiment.

Yes, I did. Now I'm serious.

Now you're serious, and up there in Congress there is a Republican majority that is going to put your experiment into practice. Are you not a little bit worried about what the results might be?

Think of it in terms of a set of choices which I want to provide for a woman. Are you going to engage in sex? Is it going to be unprotected sex? If you get pregnant, are you going to carry that baby to term? If you carry that baby to term, are you going to give the baby up for adoption? At each of those steps, there is a choice to be made. One of the things I want to happen, by getting rid of the welfare system, is not just that there'll be fewer children conceived in these circumstances, but I want a lot more of them to be given up for adoption.

The Republicans in Congress have talked about orphanages as a solution. Is this part of your thinking?

I do not now, nor have I ever advocated, taking children away from their mothers for any reason other than the ones we take them away for now.

But isn't there going to be a very strong cash reason to take them away from their mothers? They're simply not going to be able to survive with those children under your system.

You're going to have a self-selection process. It will no longer be the case, as it is now, that if you take the baby home, you'll have an apartment, food and medical care. The young women who take their babies home will be the ones who have either managed to enlist the support of their own relatives or that of the father of the baby, and are therefore likely to be the best mothers. But to the nub of the issue: after you've had the adoptions, reduced the number of pregnancies, had the self-selection process, are you going to have women who take home babies and who are not able to care for them financially? The answer is yes.

So what happens?

This is the point at which you have, as an object of historic sympathy, a child. And you also have, at the end of the 20th century, a society of immense wealth. The private sector can take care of it. I know there will be sighs of frustration - how can this man really believe that? But at the end of the day, are we going to have more children suffering under the system I propose or under the system we have right now?

I'd like to move to the second part of your thesis, as presented in The Bell Curve, where you have put something new into the equation, the social group who are destined to be failures in our cleverer, more intellectual society because their IQ is too low.

What we argue is that if you're at the low end of the IQ spectrum, life is getting tougher and tougher. Muscles aren't worth what they used to be. And the transformation in social signals has made it a lot harder if you're at the low end of the scale because life is a lot more complicated than it used to be.

Why are you so convinced that success in life and IQ are closely and deterministically related? I know lots of relatively well off people who don't have a high IQ.

We don't think there's an exact correlation, either. We are talking about statistical tendencies.

What has caused a storm is the way you link people at the bottom of the IQ scale with blacks.

The relationship between heredity and IQ in human beings is well established. But that does not mean that if you have a group difference, an ethnic difference, that difference must also be genetic. One of the major statements in The Bell Curve is that it doesn't make a lot of difference whether the reason is genetic or not. People seem to think that if the difference is caused by the environment, that's good news because we can fix it, whereas if the difference is caused by genes, that's terrible. But just because the difference is caused by the environment doesn't mean it's meaningless, and doesn't mean it's easy to fix.

It might mean much bigger social programmes. It might be a liberal left conclusion for a liberal left social agenda.

Absolutely true. Indeed, you might take this entire book and say it is a justification for a Rawlsian state, where we would redistribute because people come up on the short end of the IQ stick for no fault of their own. That said, we thought that a discussion of genes and race would help defuse the issue. In the short term, we were certainly wrong. There's been an eruption.

You were wrong to say it?

In the short term. But in the long term, I think we will prove to have lanced a boil in this country.

Let's come to the question of solutions, and where you think America's going. You've argued that there's something called dysgenesis; that if we carry on like this, then America is going to get stupider.

There's a downward pressure.

There's a downward pressure because people at the bottom end are, to put it brutally, breeding more than people at the top end. Now what I don't understand is that, if that were the case, why are IQ rates going up, not down?

The IQ rate going up or down is not necessarily a function of intelligence as such.

But you base an awful lot of the book on IQ tests.

That's one of the reasons why, when we talk about dysgenesis, we don't say that the population is getting stupider, because you have counter- vailing trends. What we say is that if you have more parents with low IQs having babies than parents with high IQs, you have a downward pressure that has to contend with a variety of other factors at work.

But this is where it connects, in most people's minds, with your agenda on welfare. They say you are merely reviving the old social Darwinist agenda that there are stupid people at the bottom, and you would like them to die out as a group because they're holding America back.

There is one sentence in the last chapter which says, mildly, that we are in favour of getting rid of these programmes. I'm trying very hard to get at a genuine problem. If you take somebody at the low end of the scale, we know we can give them enough money to get them above the poverty line. That's a mere matter of distributing a sufficient number of pound notes. The question is, how do you structure society so that person has an important and valued place in the community?

So you regard these people at the bottom as important and valued people?

Yes.

You're not saying that they're causing a problem for America?

We are saying that the key thing is not to get enough money into these people's hands, but to ensure that when they reach the age of 70, they are proud of who they have been and what they have done.

l This interview is based on extracts from `The Battle for Ideas', to be shown at 6pm on Saturday 18 March on BBC2.